Is it OK to compost non-organic food waste?

“the Centers for Disease Control and Prevention’s national bio-monitoring program has detected pesticides in blood and urine samples from 96 percent of more than 5,000 Americans age 6 and older.”

Why does this matter? Well, pesticides are toxic by design. Their purpose is to kill pests (insects, fungi and plants) on crops. Numerous studies have shown that pesticides are toxic to humans when digested or inhaled.

Where do these pesticides come from?

Food residues are the dominant source of pesticide exposure. Research has shown that pesticide levels drop when people switch to an all-organic diet and increase again after returning to conventionally grown foods (Chensheng Lu et al., 2008, ehp.niehs.nih.gov/1408197). And remember, these studies are on fully washed fruits and vegetables. Pesticides and insecticides leaves toxic residues on conventionally grown produce that cannot be removed by simply washing.

Growing food organically at home is a great way to control and reduce the levels of pesticides and insecticides in your fruits and veggies. But, if you want to grow healthy, organic food in your garden (and who doesn’t?!), should you avoid putting non-organic food scraps into your bokashi composter?

Do pesticides and toxins persist in compost?

Food scraps and peelings from non-organic produce and non-organic processed food will invariably contain pesticide residues. So, is it OK to add these to your bokashi composter? Or will these pesticides persist through to your garden soil and future garden produce?

– The good news

Fortunately, the vast majority of pesticides do break down during composting. Research studies and experts agree that any levels detectable in finished compost are typically at very low concentrations.

A literature review on pesticide bio-degradation published in 2000 in Compost Science & Utilization showed that most pesticide categories decomposed moderately well to well during traditional composting. None of the composts in this review exceeded levels considered hazardous to human health.

Similarly, John Reganold, professor of soil science and agro-ecology at Washington State University and founder of the nation’s largest certified organic teaching farm stated that:

“The heat and microbial action in most compost piles break down many produce pesticides. The pesticides remaining in the finished compost are often diluted to very low levels once mixed with soil. There can be absorption of some remaining pesticides by plants, but concentrations in the plant should be extremely low and not an issue for concern. Finally, getting the produce trimmings composted and back in the soil promotes healthy soil.

Experts agree that the majority of residual toxins in finished compost and soil cannot be absorbed by plant roots. This is comforting to know for anyone worried about pesticides from food residues in your compost. Any persistent toxins are likely to remain in the soil rather than taken up into plants and your homegrown produce.

The risk of toxins persisting in the finished compost product is fair outweighed by the benefits of composting.

In fact, compost is often added to contaminated sites to restore the soil quality and actually remove contaminants. Sites contaminated with semivolatile and volatile organic compounds (VOC’s), such as petroleum fuels and explosives, can actually be cleaned up by adding compost. In addition, compost can bind heavy metals and prevent these from being absorbed by plant roots.

– The bad news

There are a few compounds in pesticides that are known to persist in the environment and not degrade in compost. After the environmental disaster that was DDT, it is incredible that pesticides which resist degradation are still in production!

One of the most widely known examples is Clopyralid; a lawn weed killer. It does not break down during composting. Fortunately, unlike DDT, Clopyralid does not accumulate in animal tissues. As such, unlike DDT, it is not passed along the food chain. However, it is very mobile in both water and soil, and can pass through cattle unchanged. This means that Clopyralid could show up in your compost and garden, even if you have not used it yourself.

Nightshades, legumes and Asteraceae are particularly sensitive to clopyralid. So, avoid using compost made from grass clippings or cow manure that may have been treated with Clopyralid products. Especially if you plan on growing legumes, peppers or sunflowers.

A newer group of pesticides are becoming increasingly wide spread; Neonicotinoids. Research has shown that these new pesticides are highly toxic to honeybees and other pollinators. A recent review of human health research concluded that existing studies into Neonicotinoids are incomplete. In other words, there is still a lot we don’t know about some pesticides.

How Compost Degrades Pesticides

The likelihood of pesticides being broken down is affected by the composting method used. The more numerous and diverse the active microorganisms in the compost feed stock, the greater the chance that a pesticide will encounter a microbe that can degrade it. Composting food scraps with bokashi, ensures that any pesticides are bombarded by billions of microbes.

Pesticide levels reduce by a variety of processes during the composting (Ohio State University, Factsheet):

Decay: The break down of toxins into simpler (non-toxic) molecules.

Volatize: When toxins escape into the atmosphere through evaporation.

Adsorption: Some toxins bond with other compounds to form non-toxic compounds.

Leaching: Some soluble toxins can be simply washed out of compost.

Humification: Humification occurs when toxins combine with humus to become part of the humus molecules.

Mineralization: This is the preferred end point for pesticides and defines the break down of toxins into their inorganic and organic elements. This process results in stable, permanent non-toxic molecules; CO2, water and minerals.

Note that not all of these processes reduce the total concentration of toxins. For example, volatilization and leaching just move the toxins to other parts of the environment. Similarly, adsorption does not destroy the toxin it simply transforms it into a state that is no longer bio-available for as long as the compound exists. If the compound breaks down, the pesticide will be released into the environment again. As such, the preferred end point for pesticides is mineralization. Mineralization results in the pesticides being permanently broken down.

So… should you put non-organic food scraps in your bokashi composter?

Yes! Go ahead and put non-organic produce in your bokashi composter. Although there is a risk that trace toxins may be detectable in the final compost, the benefits of composting far outweigh this small risk. Making compost is a smart thing to do for your garden, and for the environment.

The vast majority of pesticide toxins are known to break down during composting. Experts agree that microbes play a crucial role in this. The more microbes that a toxin encounters, the more likely it is to be broken down. Bokashi compost is richer in effective microbes than any other form of composting. This means that bokashi a great way to remove toxins from non-organical food waste.